The Aristo U25B and SD45 locos exhibit different speeds when run separately on a track with the same power applied. This condition is apparently due to different gearing and / or electric motor characteristics within their power trucks. None-the-less these locos can be operated together in an “MU” lash up whilst pulling a load such as a train. (It is to be appreciated that the U25B shares the same motor block design with other Aristo 2 axle locos that include the FA1 / FB1, RS3, RDC1, and Eggliner, and as such one can expect very similar results.)

To see how the different locos work together, I setup a test train that consisted of 25 cars.The U25B pair did not pull this train without incurring wheel slip on certain parts of my circuitous under house layout that includes mostly 10 foot diameter curve tracks. The single SD45 will pull the train all by itself without any apparent wheel slip.(For folks who have layouts with long straight track sections and / or very wide diameter curves or have installed additional weights to the locos, longer trains can be pulled than my example described here.)

The following pictures depict a consist of Aristo-Craft locos including 2 U25Bs of the older motor block design and an SD45 pulling a 25 car train on my under house layout. This is to illustrate how the speed difference of the U25Bs (being generally faster) work with the SD45 when operating with the 2 U25Bs as lead units, then the trio swapped around when operating with SD45 as the lead unit:

Below is shown the Aristo-Craft loco operation whilst pulling the train with the two SP U25Bs leading the SD45 trailing unit. The U25Bs are of the NON ball bearing motor block types:

The below picture shows the coupling of a U25B to the SD45:

Below is shown the locos with swapped direction with the train being pulled by the leading SP SD45 coupled to two U25Bs:

Below is shown the top views of the coupler action between the U25B and SD45:(The camera auto focus did not work too well here, but it is still good enough to see the coupler action):

Aristo-Craft loco operation of two SP U25Bs leading an SD45 showing the coupler action at the U25B & SD45 whilst pulling a 25 car train:

Shown below is the SP SD45 now leading the 2 U25Bs and showing the coupler action at the SD45 & U25B whilst pulling the same train: (Note there is no apparent coupler binding or sideways forces.)

Given the coupler action pictures, it does not appear to matter as to placement of the "faster" U25B locos.Close observation of the wheel sets of all locos show no slippage when starting out or pulling the test train.The train load appears to integrate the locos' speed difference operation.In this regard, It would seem that the U25Bs may draw slightly more current and the SD45 may draw slightly less current under such collective operation.In any event, the track power amp meter shows little current use (approx. 2 amps or less) whilst operating the test train at various speeds no matter which way the trio of locos are oriented.

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Comment: Aristo’s U25B stability and is truck mount design.

Some folks have described Aristo's U25B as having a stability problem. This may manifest itself in the loco exhibiting a wobble or listing to one side, particularly when the loco is operated on curves. Since my U25Bs don’t have too much operational time on them, I have yet to experience this. However, looking at how this loco is designed by Aristo, it appears to have something to do with its rather odd truck pivot design. This is a design that resembles Aristo's passenger car trucks - that being the offset pivot, but the U25B loco has an added plastic adapter plate inclusive of a 4 metal roller arrangement to apparently reduce friction when the trucks pivot. This offset pivot arrangement is of benefit for tight curve train operation by reducing the amount of front and rear overhang at the coupler ends of the loco that projects toward the outside of the curve, albeit with the trade-off of a bit more belly overhang.That said, it seems some folks with this loco have experienced a wobble or list to one side when rounding curves - maybe because of those rollers wearing or falling out or the wear done to the under side plastic surface of the loco's frame as the rollers traverse this area. Something else to consider is that adding more weight within the fuel tank area can be expected to improve the loco’s stability as well as its traction.

The below pictures are of my Union Pacific U25B that happens to have the newer ball bearing type motor blocks. However, this is not relevant to the offset pivot hardware since all U25B incorporate this design feature.

The pictures may also help with respect to seeing where lubrication can be applied, however, be advised from my experience that the use Aristo's Electralube has been associated with cracked plastic journals on other Aristo rolling stock.

As shown below, the Aristo-Craft U25B loco uses an adapter plate with pivot rollers to implement an offset mounting of its 2 axle power truck. This design affords a shorter coupler end overhang with the trade-off of more belly overhang that is helpful on tighter curves.